0138-Copy-List-with-Random-Pointer.py

'''
A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.

Return a deep copy of the list.

The Linked List is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val, random_index] where:

    val: an integer representing Node.val
    random_index: the index of the node (range from 0 to n-1) where random pointer points to, or null if it does not point to any node.

 

Example 1:

Input: head = [[7,null],[13,0],[11,4],[10,2],[1,0]]
Output: [[7,null],[13,0],[11,4],[10,2],[1,0]]

Example 2:

Input: head = [[1,1],[2,1]]
Output: [[1,1],[2,1]]

Example 3:

Input: head = [[3,null],[3,0],[3,null]]
Output: [[3,null],[3,0],[3,null]]

Example 4:

Input: head = []
Output: []
Explanation: Given linked list is empty (null pointer), so return null.

 

Constraints:

    -10000 <= Node.val <= 10000
    Node.random is null or pointing to a node in the linked list.
    Number of Nodes will not exceed 1000.
'''
"""
# Definition for a Node.
class Node:
    def __init__(self, x: int, next: 'Node' = None, random: 'Node' = None):
        self.val = int(x)
        self.next = next
        self.random = random
"""
class Solution:
    def copyRandomList(self, head: 'Node') -> 'Node':
        if not head:
            return None
        
        copy = {}
        cur = head
        while cur:
            copy[cur] = Node(cur.val, None, None)
            cur = cur.next
        cur = head
        while cur:
            if cur.next:
                copy[cur].next = copy[cur.next]
            if cur.random:
                copy[cur].random = copy[cur.random]
            cur = cur.next
        return copy[head]